Sterol additive in asphalt pavement

ABSTRACT

Pavement aging can be reduced by applying to an asphalt-containing pavement a topcoat layer or a surface treatment containing asphalt binder with sterols.

BACKGROUND

Asphalt pavement is a composite material that is a mixture of mineralaggregate and a liquefied asphalt (bitumen) binder, which hardens toform a robust surface. The bitumen is generally liquefied throughheating. Asphalt pavements can also be produced using bitumen that hasbeen blended with solvents (known as cutbacks) or bitumen that has beendispersed in water (known as asphalt emulsions). Asphalt pavements caninclude reclaimed or recycled materials containing reclaimed asphaltpavements (RAP), reclaimed asphalt shingles (RAS), ground tire rubber,and other post-consumer waste materials. Asphalt pavement deterioratesover time from oxidation of asphalt binder, heavy loads, moisture damageand varying climatic conditions resulting in fatigue cracking which thenfurther accelerates the deterioration of the overall pavement.

Methods for restoring or repairing deteriorated asphalt pavement includeremoving and replacing the existing pavement with either newly preparedor recycled pavement. The lifetime of existing pavement may also beextended by applying certain surface treatments.

SUMMARY

Disclosed is a method of using sterol in asphalt compositions andmethods that may be used for constructing a topmost portion of thepavement and surface treatments for pavement preservation andmaintenance. The disclosed sterol-containing asphalt binder can retard,reduce or otherwise overcome the effects of aging in asphalt so as topreserve or retain some or all of the original properties of the virginbinder or virgin asphalt originally used when laying down the asphalt.

In one embodiment is a method of road paving comprising:

-   -   providing sterol-containing asphalt binder, wherein sterol is        added to an asphalt binder from 0.5 to 15 wt. % of the sterol        based on the asphalt binder;    -   combining the sterol-containing asphalt binder with aggregate to        form an asphalt paving material;    -   applying the asphalt paving material atop an asphalt pavement        layer; and    -   compacting the applied asphalt paving material to form a road        pavement having a sterol-containing topcoat layer.

In another embodiment is disclosed a method for treating anasphalt-containing surface comprising:

providing a surface treatment comprising sterol-containing asphaltbinder, wherein sterol is added to an asphalt binder from 0.5 to 15 wt.% of the sterol based on the asphalt binder; and

applying the surface treatment to the surface of an existing pavement.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A depicts an asphalt pavement structure.

FIG. 1B depicts the asphalt pavement structure of FIG. 1A with a surfacetreatment.

FIG. 1C depicts the asphalt pavement with an interlayer.

FIG. 2 graphically depicts m-critical compared to days of oven aging at75° C.

FIG. 3 graphically depicts S-critical compared to days of oven aging at75° C.

FIG. 4 graphically depicts ΔTc compared to days of oven aging at 75° C.

FIG. 5 graphically depicts R-value compared to days of oven aging at 75°C.

FIG. 6 graphically depicts high temperature PG grade at 1.0 kPa comparedto days of aging at 75° C.

FIG. 7 graphically depicts S-critical and m-critical properties ofbinder recovered from the top and second half inch of compactedspecimens after 60 days of oven aging.

FIG. 8 graphically depicts ΔTc and R-Value properties of binderrecovered from the top and second half inch of compacted specimens after60 days of oven aging.

FIG. 9 graphically depicts S-critical and m-critical properties ofbinder recovered from the top and second half inch of compactedspecimens after 152 days of oven aging.

FIG. 10 graphically depicts ΔTc and R-Value properties of binderrecovered from the top and second half inch of compacted specimens after152 days of oven aging.

DETAILED DESCRIPTION

Disclosed is the use of sterols in compositions and methods that may beused for pavement construction or pavement preservation and maintenance.Applicants have previously shown that sterols can retard, reduce orotherwise overcome some of the effects of asphalt aging so as topreserve or retain some or all of the original properties of virginasphalt binder. See International Application Nos. PCT/US16/037077,PCT/US16/64950 and PCT/US16/064961, PCT/US17/045887 each of which isincorporated herein by reference in its entirety. The sterol wasparticularly effective when the binders contained reclaimed or recycledmaterials such as RAP, RAS or combinations of both; or when the bindercontained paraffinic additives such as paraffinic base oils orre-refined engine oil bottoms (REOB) which are often used to softenbinders.

Headings are provided herein solely for ease of reading and should notbe interpreted as limiting.

Abbreviations, Acronyms & Definitions

“Aged” refers to hard, poor-quality, or out-of-specification virginasphalt or virgin binder, particularly virgin binders having aring-and-ball softening point greater than 65° C. by EN 1427 and apenetration value at 25° C. by EN 1426 less than or equal to 12 dmm.

“Aggregate” and “construction aggregate” refer to particulate mineralmaterial such as limestone, granite, trap rock, gravel, crushed gravelsand, crushed stone, crushed rock and slag useful in paving and pavementapplications.

“Asphalt” refers to a binder and aggregate and optionally othercomponents that are suitable for mixing with aggregate and binder.Depending on local usage, the terms “asphalt mix” or “mix” may be usedinterchangeably with the term “asphalt.”

“Binder” refers to a highly viscous liquid or semi-solid form ofpetroleum. “Binder” can include, for example bitumen. The term “asphaltbinder” is used interchangeably with the term “binder.”

“Bitumen” refers to a class of black or dark-colored (solid, semisolid,or viscous) cementitious substances, natural or manufactured, composedprincipally of high molecular weight hydrocarbons, of which asphalts,tars, pitches, and asphaltenes are typical.

“Crude” when used with respect to a material containing a sterol meanssterol that has not been fully refined and can contain components inaddition to sterol.

“m-critical” or “Creep critical” grade refers to the low temperaturerelaxation grade of a binder. The creep critical temperature is thetemperature at which the slope of the flexural creep stiffness versuscreep time according to ASTM (the Bending Beam Rheometer (BBR) test hasan absolute value of 0.300. The creep critical temperatures can also bedetermined from a 4 mm Dynamic Shear Rheometer (DSR) test at a value of−0.275.

“Neat” or “Virgin” binders are binders not yet used in or recycled fromasphalt pavement or asphalt shingles, and can include Performance Gradebinders.

“Pure” when used with respect to a sterol or mixture of sterols meanshaving at least a technical grade of purity or at least a reagent gradeof purity.

“Reclaimed asphalt” and “recycled asphalt” refer to reclaimed asphaltpavement, reclaimed asphalt shingles, and reclaimed binder from oldpavements, shingle manufacturing scrap, roofing felt, and otherasphalt-containing products or applications.

“Reclaimed asphalt pavement” and “RAP” refer to asphalt that has beenremoved or excavated from a previously used road or pavement or othersimilar structure, and processed for reuse by any of a variety ofwell-known methods, including milling, ripping, breaking, crushing, orpulverizing.

“Reclaimed asphalt shingles” and “RAS” refer to shingles from sourcesincluding roof tear-off, manufacture's waste asphalt shingles andpost-consumer waste.

“S-Critical” or “stiffness critical” grade refers to the low temperaturestiffness grade of a binder. The stiffness critical temperature is thetemperature at which a binder tested according to ASTM D6648 has aflexural creep stiffness value of 300 MPa or as determined by either theBending Beam Rheometer test or 4 mm DSR test as described in ΔTc.

“Softening agent” refers to low viscosity additives that ease (orfacilitate) the mixing and incorporation of a recycled binder intovirgin binder during an asphalt production process.

“Sterol additive” refers to sterols or sterol mixes that can be combinedwith binder to retard the rate of aging of asphalt or binder, or torestore or renew aged asphalt or aged binder to provide some or all ofthe original properties of virgin asphalt or virgin binder.

“Sterol blend” refers to a composition, mixture or blend of pure sterolsand crude sterols that can be combined with aged binder (e.g. recycledor reclaimed asphalt) to retard the rate of aging of asphalt binder, orto restore or renew the aged binder to provide some or all of theoriginal properties of virgin asphalt or virgin binder.

“ΔTc” refers to the value obtained when the low temperature creep orm-value critical temperature is subtracted from the low temperaturestiffness critical temperature. The 4 mm dynamic shear rheometer (DSR)test and analysis procedures are described by Sui, C., Farrar, M.,Tuminello, W., Turner, T., A New Technique for Measuring low-temperatureProperties of Asphalt Binders with Small Amounts of Material,Transportation Research Record: No 1681, TRB 2010. See also Sui, C.,Farrar, M. J., Harnsberger, P. M., Tuminello, W. H., Turner, T. F., NewLow Temperature Performance Grading Method Using 4 mm Parallel Plates ona Dynamic Shear Rheometer. TRB Preprint CD, 2011, and by Farrar, M., etal., (2012), Thin Film Oxidative Aging and Low Temperature PerformanceGrading Using Small Plate Dynamic Shear Rheometry: An Alternative toStandard RTFO, PAV and BBr. Eurasphalt & Eurobitume 5th E&ECongress-2012 Istanbul (pp. Paper O5ee-467). Istanbul: FoundationEuraspalt.

All weights, parts and percentages are based on weight unless otherwisespecified.

FIG. 1 is a cross-section of a portion of a typical asphalt pavement.Crushed aggregate is applied as a base course atop a subgrade, which maybe soil. The crushed aggregate base course may for example have anaverage thickness of about 152 mm (6 inches) to about 305 mm (12inches). Atop the aggregate base course can be applied one or moreasphalt layers. FIG. 1 illustrates two asphalt layers, referred to as anasphalt pavement underlayer and an asphalt pavement topcoat. The asphaltpavement underlayer may for example have an average thickness of about57 mm (2.25 inches) to about 305 mm (12 inches) paved in several lifts,or 57 mm (2.25 inches) to about 127 mm (5 inches) paved in severallifts; and the asphalt pavement topcoat may for example have an averagethickness of about 38 mm (1.5 inches) to about 102 mm (4 inches) or 38mm (1.5 inches) to 63 mm (2.5 inches). It should be noted that thethickness is also dictated by the maximum aggregate size.

The terms “underlayer” and “topcoat” that qualify the asphalt layersshould be understood as relative terms. The further the asphalt layer isfrom the base course, the more “top” the asphalt layer is considered.The topmost asphalt layer—topcoat is exposed to weather and the elementssuch as sun, rain, snow, and freezing and thawing. The pavement alsoexperiences frictional wear, fractures and other damage due to vehiculartraffic. Over time, these environmental and service factors cause theasphalt pavement, particularly the surface layer, to deteriorate.

Ideally, one would construct the entire pavement, namely from the basecourse up to the topmost asphalt layer, with sterol-containing asphaltpaving materials because over time the asphalt layers age. Aging is notlimited to the uppermost portion of the asphalt pavement (e.g., theuppermost 38 mm to 65 mm of compacted pavement). However, the asphaltbinder tends to age most severely at the surface, and the degree ofaging and consequent detrimental impact on the binder typicallydecreases with pavement depth, and without regard to the materials thatmay have been added to the binder or other components of the pavingmaterial.

Although a sterol may be added to an entire asphalt pavement, sterolsare somewhat expensive. To control costs, however, the topmost asphaltlayer or layers can be paved with sterol-containing asphalt binderpaving material. Doing so can retard binder aging throughout the asphaltpavement by making the topcoat layer more resistant to aging andmeanwhile protecting the underlying asphalt pavement for an extendedtime period from weather, elements and other damage caused by prematuredeterioration of the topcoat layer. For example, by retarding asphaltaging, particularly in the topmost layer or layers, surface crackingthat is associated with aged binders can be reduced thereby reducing airmovement into the underlying pavement and the associated oxidation.Similarly, by retarding asphalt aging in the topmost layer or layers,moisture uptake in the topcoat layer and moisture transmission throughthat layer or through cracks in that layer can be reduced, therebylimiting further damage to the pavement and increases in its aging rate.By lengthening the time at which the binder reaches a condition wherepavement distress begins the overall pavement life is improved.

When a pavement is to be resurfaced, one might mill away, for examplethe upper 76 mm (3 inches) to 102 mm (4 inches) of old pavement andreplace part or all of the milled portion with a sterol-containingreplacement portion. The replacement portion can be applied in manydifferent configurations such that only the topmost 12 mm (0.5 inches)to 19 mm (0.75 inches) or the topmost 12 mm (0.5 inches) to 38 mm (1.5inches) is applied as a thin overlay that contains a binder with sterol.For example, two 38 mm lifts may be applied with only the topmost 38 mmincluding a binder with sterol. As another example, the milled out 76 mm(3 inches) or 102 mm (4 inches) can be replaced with two 50 mm (2 inch)lifts or a 50 mm (2 inch) lift with a 25 mm (1 inch) thin overlay (viz.,a thinlay), with only the topmost lift or overlay including a binderwith sterol.

Other compositions and methods for addressing pavement deteriorationinclude preserving and maintaining an existing pavement with the aid ofsterol-containing surface treatments disclosed herein. In suchtreatments, sterols may be employed as an asphalt blend component insurface treatments for pavement preservation.

Asphalt surface treatment is a broad term embracing several asphalttypes and asphalt-aggregate applications that may be used to extend thestructural life of the underlying pavement. Such surface treatmentsusually are less than 25 millimeter (1 inch) thick and may be applied toany kind of road surface. The road surface may for example be a primedgranular base, or an existing asphalt or Portland cement concretepavement. Surface treatments applied to an existing pavement surface areoften called seal coats. Surface treatments commonly called chip sealsare applied by spraying an asphalt emulsion and immediately spreadingand rolling onto the applied emulsion an aggregate cover. A sandwichseal is another surface treatment technique, in which a large aggregateis placed first, an asphalt emulsion (normally polymer modified) issprayed onto the aggregate, and immediately followed by an applicationof smaller aggregate on top of the emulsion to lock in the seal. A Capeseal is a single surface treatment followed by a slurry seal ormicro-surfacing layer to fill in the voids. These and other surfacetreatments may be applied multiple times as desired. In someembodiments, the sterol-containing asphalt binder can be applied as atack coat and as a fog seal.

Taking into consideration factors such as the region and climate,surface treatments that include sterol-containing asphalt binder may beapplied as an emulsion, hot applied bitumen or cutback. In all cases,the bitumen used in the surface treatment can contain polymer additivesderived from classes such as styrene butadiene rubber (SBR) lattices,styrene butadiene styrene (SBS) block copolymers, reactive ethyleneterpolymers (RET), ground tire rubber, acrylic lattices, neoprenelattices, ethylene vinyl acetate (EVA) and polybutene. This list shouldnot be taken as limiting because any polymer that can be incorporatedinto asphalt in hot, cutback or emulsified form is a candidate. Somesurface treatments are based solely on asphalt emulsions as the binder(for example slurry seals and micro-surfacing). Chip seals can beconstructed using an emulsion, hot applied asphalt binder, or cutbackasphalt. The choice of binder type to use for chip seals is oftendictated by the region or climate. The addition of sterol to any ofthese treatments can favorably impact binder aging in the surfacetreatment, thus prolonging the useful life of the surface treatmentwhich in turn provides extended protection against aging for pavementbeneath the surface treatment.

Whatever pavement construction process is used, the primary ingredientsinclude sterol additive added to a binder.

Sterol Additive

The disclosed sterol additives preferably can alter (e.g., reduce orretard) an asphalt binder aging rate, or can restore or renew an aged orrecycled binder to provide some or all of the properties of a virginasphalt binder. The disclosed compositions and methods use a class ofplant-derived chemistry, the sterol class of compounds. While plantsterols do not contain the same number of condensed or partiallyunsaturated rings as asphaltenes, they do have the benefit of not beinga linear or branched linear molecule. For example, a sterol can alter orimprove physical and rheological characteristics such as stiffness,effective temperature range, and low temperature properties of anasphalt binder.

In some embodiments, the sterol additive belongs to the class oftriterpenoids, and in particular to sterols or stanols. The disclosedsterols (e.g. triterpenoids) can effectively work with asphaltenes.Asphaltenes include extensive condensed ring systems with some level ofunsaturation. The asphaltene content of typical binders can range fromless than 10% to more than 20%. Asphaltenes are typically described asmaterials that are insoluble in n-heptane. An exact structure is unknownand based on the performance behavior of different binders it isunlikely that the asphaltene structure in any two binders is the same,especially those from different crude sources. Asphaltenes give a binderits color and stiffness and they increase in content as the binder ages.Consequently, the addition of RAP and/or RAS causes the asphaltenecontent to increase. Increasing asphaltene content along with otherproducts of oxidation such as carbonyls and sulfoxides are responsiblefor the stiffening of bituminous mixtures and their ultimate failure. Bytheir very chemical nature asphaltenes are not readily soluble inaliphatic chemicals. Aromatic solvents will readily dissolve asphaltenesand aromatic process oils have been used in recycled mixtures. However,these oils may contain polynuclear aromatic compounds including listedpotential carcinogens and therefore are not desirable additives. Mostplant based oils are straight or branched chain hydrocarbons with somelevel of unsaturation and therefore are not as effective at retardingaging as they are at softening the overall binders in a mixture.

Triterpenoids are a major group of plant natural products that includesterols, triterpene saponins, and related structures. Triterpenoids canbe natural or synthetic. Typically, they are obtained by extraction fromplant material. Extraction processes for the isolation of triterpenoidsare described e.g. in international application publication numbers WO2001/72315 A1 and WO 2004/016336 A1, the disclosures of which are eachincorporated herein by reference in their entirety.

The triterpenoids include plant sterols and plant stanols. The disclosedtriterpenoids include the esterified and non-esterified forms of any ofthe plant sterols mentioned herein.

Exemplary pure plant sterols include campesterol, stigasterol,stigmasterol, β-sitosterol, Δ5-avenosterol, Δ7-stigasterol,Δ7-avenosterol, brassicasterol or mixtures thereof. In some embodiments,the sterol blend contains β-sitosterol as the pure sterol. In otherembodiments, the sterol blend contains a mixture of pure sterols.Commercially available pure sterols and mixtures of pure sterols includethose available from MP Biomedicals (Catalog No. 02102886) referred toas beta-Sitosterol (beta-Sitosterol ˜40-60%; campesterol ˜20-40%;Stigmasterol ˜5%). In some embodiments, the pure sterol can include purecholesterol. Cholesterol is shown here to have similar effects as plantsterols.

In some embodiments, a pure sterol can have at least 70 wt. % sterols,and in some embodiments can have at least 80 wt %, at least 85 wt % orat least 95 wt % sterols.

Exemplary crude plant sterols include modified or unmodified naturalproducts containing significant quantities of sterols, including suchdiverse plant sources as corn oil, wheat germ oil, sarsaparilla root,soybean pitch and corn oil pitch. For example, tall oil pitch can beobtained indirectly from the process of preparing paper from wood,particularly pine wood. For example, tall oil is a product of woodpulping (for example by the Kraft process), of which tall oil pitch is aby-product of the distillation of tall oil. Tall oil pitch is anextremely complex material that can contain rosins, fatty acids,oxidation products and esterified materials, an appreciable fraction ofwhich are sterol esters. Plant sources of crude sterols are inexpensivein that they are the foots or tailings left from various manufacturingprocesses.

In some embodiments, the crude sterol sources include stigmasterol,β-sitosterol, campesterol, ergosterol, brassicasterol, cholesterol andlanosterol or mixtures thereof. In some embodiments, the crude sterolsources include soybean oil, corn oil, rice bran oil, peanut oil,sunflower seed oil, safflower oil, cottonseed oil, rapeseed oil, coffeeseed oil, wheat germ oil, tall oil, and wool grease. In someembodiments, the crude sterol includes a bio-derived source or partiallydistilled residue of the bio-derived source. In some embodiments, thecrude sterol source includes tall oil pitch, soybean oil or corn oil.

Any of the oil tailings or pitches from the disclosed plant sources aresuitable crude sterol sources. U.S. Pat. No. 2,715,638, Aug. 16, 1955,to Albrecht, discloses a process for recovering sterols from tall oilpitch whereby the fatty acid impurities are removed by a neutralizationprocess. Following this, the sterol esters are saponified; the freesterols are then recovered and washed with isopropanol and dried.

The crude sterols preferably are obtained from plant sources. The crudesterol can include components in addition to the desired sterol orsterols. Exemplary plant sources for crude sterols include tall oilpitch, crude tall oil, sugar cane oil, hot well skimmings, cottonseedpitch, soybean pitch, corn oil pitch, wheat germ oil or rye germ oil. Insome embodiments, tall oil pitch is a source of the crude sterol. Talloil pitch can include about 30 to 40% unsaponifiable molecules.Unsaponifiables are molecules that do not react with alkali hydroxides.Fatty and rosin acids remaining in the tall oil pitch readily react withpotassium or sodium hydroxides and thus the unsaponifiables can bereadily separated. It has been shown that 45% of the unsaponifiablefraction can include sitosterols. Therefore, a tall oil pitch sample cancontain approximately 13.5% to 18% sterol molecules by weight. In someembodiments the crude sterol can have less than a food grade of purity(e.g., less than 85 wt. % sterols) or contain more than 85 wt. % sterolsbut also can contain impurities or contaminants that render the materialunsuitable for use in foods.

In some embodiments, the crude sterol may be animal derived. In someembodiments, the crude sterol is cholesterol.

It should be understood that the disclosed sterol can be used in anycombination that includes animal derived, plant derived, pure or crude.For example, in some embodiments the sterol is pure sterol from plants.In some embodiments, the sterol is pure sterol that is a combination ofplant derived and animal derived. In some embodiments, the sterol iscrude sterol from a combination of plant derived and animal derived.

The sterol added to the asphalt binder may for example range from about0.5 to about 15 wt. %, from about 1 to about 10 wt. %, or from about 1to about 3 wt. % of the binder in an asphalt. In some embodiments, thesterol added to the asphalt binder may for example range from about 0.5to about 15 wt. %, from about 1 to about 10 wt. %, or from about 1 toabout 3 wt. % of a virgin binder in an asphalt.

In some embodiments, the sterol is a sterol blend in which the puresterol:crude sterol blend added to an asphalt binder may for examplerange from about 0.5 to about 15 wt. %, or about 1 to about 10 wt. %,about 1 to about 3 wt. % of the virgin binder in an asphalt composition.The sterol blends, in some embodiments include a 10:90 to 90:10 ratio ofpure sterol to crude sterol. The sterol blends in some embodimentsinclude at least a 20:80, 30:70 or 40:60 ratio of pure sterol to crudesterol, and in some embodiments include less than an 80:20, 70:30 or60:40 ratio of pure sterol to crude sterol.

In some embodiments, sterol can alter, reduce or retard the degradationof rheological properties due to aging in binders containing recycledbituminous materials such as RAS and/or RAP combined with softeningagents such as, REOB, virgin paraffin or naphthenic base oils, untreatedor non-rerefined waste drain oils or waste engine oil materials, vacuumtower asphalt extenders, paraffinic or naphthenic processing oils orlubricating base oils.

In some embodiments, sterol can alter, reduce or retard the degradationof rheological properties due to aging in binders containing recycledbituminous materials such as RAS and/or RAP combined with softeningagents such as bio-derived oils or additives. Such bio-dereived oils oradditives include oils or esters from natural or biological resources,including derivatives or modifications thereof. Non-limiting examples ofbio-derived oils or additives include one or more of a vegetable oil orester thereof, a seed oil or ester thereof, a soybean oil or esterthereof, a corn oil or ester thereof, a cashew oil or ester thereof, apalm oil or ester thereof, a canola oil or ester thereof, a saffloweroil or ester thereof, a sunflower oil or ester thereof, a citrus oil orester thereof, pine oil or ester thereof, a rosin oil or ester thereof,or a bio-derived fatty acid ester. Exemplary commercially availablebio-derived oils or additives include those available from CargillIncorporated under the Agri-Pure Gold™ brand (such as Agri-Pure Gold 53,55, 63S, 67, 135, 142S, 200, 500, 750S, and 2000) and the Anova™ brandasphalt bio-derived agents.

In embodiments, the sterol can alter, reduce or retard the degradationof rheological properties due to aging in binders containing recycledbituminous materials such as RAP, RAS, combinations of both RAP and RAS,or softening agents with RAP, RAS, or combinations of both RAP and RAS.

Binders

The binders used can include any binder known in the art and from anyregion, naturally occurring or manufactured. Asphalt-based bindersinclude petroleum-based binders. Suitable asphalt-based or asphaltbinders include those binders complying with ASTM D-6373, D-3387, D-946,AASHTO M320, M332, M226, or M20.

Some asphalt paving can include recycled materials such as RAP and RASas components in the asphalt being paved. Typically, RAP concentrationscan be as high as 50% and RAS concentrations can be as high as 6% byweight of the paving mixture. The typical binder content of RAP is inthe range of 4-6% by weight and the typical binder content of RAS is inthe range of 20-25% by weight. Consequently, a mixture containing 50% byweight of RAP will contain 2.5% to 3% RAP binder contributed to thefinal binder mixture and a binder mixture containing 6% RAS by weightwill contain 1.2% to 1.5% RAS binder contributed to the final bindermixture.

The disclosed binders containing sterol can provide recycled asphalt(e.g. RAP or RAS) having improved physical and rheologicalcharacteristics such as reduced stiffness, more effective temperaturerange, and desirable low temperature properties.

Other Additives

The asphalt may contain other components in addition to the disclosedsterol-containing asphalt binder. Such other components can includeelastomers, non-bituminous binders, adhesion promoters, softeningagents, rejuvenating agents and other suitable components.

Useful elastomers include, for example, ethylene-vinyl acetatecopolymers, polybutadienes, ethylene-propylene copolymers,ethylene-propylene-diene terpolymers, reactive ethylene terpolymers(e.g. ELVALOY™), butadiene-styrene block copolymers,styrene-butadiene-styrene (SBS) block copolymers, isoprene-styrene blockcopolymers and styrene-isoprene-styrene (SIS) block copolymers,chloroprene polymers (e.g., neoprenes) and the like. Cured elastomeradditives may include ground tire rubber materials. For example, see the2015 Standard Specifications for the State of California (Section 37,pg. 423), and Section 39 for Hot Mix Asphalt, starting on pg. 447 andavailable at http://www.dot.ca.gov/dist1/d1lab/SECTION%2039%20%20HMA.pdf and http://caltrans-opac.ca.gov/publicat.htm.

The asphalt binder may be prepared by mixing or blending sterol withbinder (e.g. virgin binder) to form a mixture or blend. In someembodiments, the mixture or blend can be added to recycled asphaltmaterials (e.g. RAS and/or RAP) and aggregate. One of skill in the artwill recognize that any sequences of adding and mixing components arepossible. In some embodiments, a method of preparing an asphalt mixinvolves mixing or blending a sterol with virgin asphalt at atemperature from about 100° C. to about 250° C. or from about 130° C. toabout 200° C. In some embodiments, the sterol is mixed with the virginasphalt at a temperature from about 125° C. to about 175° C., or 180° C.to 205° C. In some embodiments, the virgin asphalt is combined withsterol and softening agent. In still other embodiments, the virginbinder is combined and mixed with sterol and aggregate to form anasphalt pavement material. In other embodiments, the virgin binder iscombined and mixed with binder extracted from RAP, RAS or a combinationof RAP and RAS, sterol and aggregate to form an asphalt pavementmaterial.

A mixture of a suitable aggregate comprising stones, gravel, sand, andthe like, is heated at an elevated temperature of about 132-187° C. andmixed with a similarly hot, asphalt binder containing sterol until theaggregate particles are coated with the binder. Paving mixes made inthis temperature range are often referred to as a hot mix. The mixtureof asphalt and aggregate is then applied by a paving machine to asurface which is usually roller compacted by additional equipment whilestill at an elevated temperature. The compacted aggregate and asphaltbinder eventually stiffens upon cooling to form a pavement.

The disclosed sterol-containing asphalt binder can be applied to thetopmost asphalt layers of a road pavement by to other process such ascold-mix process where the aggregate, cold and moist, is mixed with ahot or cold binder, which can be an emulsion of asphalt dispersed inwater using a suitable surfactant or a mixture of asphalt and a suitablehydrocarbon solvent, such as naphtha, #1 oil, or #2 oil, to name a few(generally referred to as a cutback asphalt). The emulsified asphaltparticles coat and bind with the aggregate and remain after the waterhas evaporated. When a cutback asphalt is used, the hydrocarbon solventevaporates at different rates depending on the volatility of thesolvent. Regardless of the solvent volatility, what remains behind is apaving material where the asphalt component gradually hardens orstiffens over time as the solvent is removed (e.g. by evaporation).

The binder can also be foamed and mixed with the aggregate to enhancethe coating efficacy. Some emulsions also utilize hydrocarbon solventsin addition to water to produce materials suitable for specificapplications. Warm mix processes may also be used to form a pavement inwhich the topmost asphalt layer of the pavement includes asterol-containing asphalt binder.

In one embodiment a method of making a road pavement is disclosed suchthat, a sterol-containing asphalt binder is provided wherein a sterol isadded to a virgin asphalt binder from 0.5 to 15 wt. % of the sterolbased on the virgin asphalt binder; combining the asphalt bindercontaining sterol with aggregate to form an asphalt paving material;applying the asphalt paving material atop an asphalt pavement layer; andcompacting the applied asphalt paving material to form a road pavement.In some embodiments, the asphalt paving material can be compacted toform a road pavement to a suitable density, typically 89% or greater ofmaximum theoretical density depending on aggregate gradation andposition within the pavement layer to form a road pavement.

In another embodiment, a method for treating an asphalt-containingsurface comprising providing a surface treatment comprisingsterol-containing asphalt binder, wherein sterol is added to an asphaltbinder from 0.5 to 15 wt. % of the sterol based on the asphalt binder;and applying the surface treatment to the surface of an existingpavement.

In some embodiments, the binder includes a blend of binders. In someembodiments, the binder blend includes virgin binder and binderextracted from reclaimed asphalt. For example, the binder extracted fromRAS material may be extracted from manufacturer asphalt shingle waste,from consumer asphalt shingle waste, or from a mixture of bindersextracted from manufacturer and consumer asphalt shingle waste. In someembodiments, a binder blend may include from about 60 wt % to about 95wt % of virgin binder and sterol from about 0.5 wt % to about 15.0 wt %of the virgin asphalt. In some embodiments, a binder blend may furtherinclude 5 wt % to about 40 wt % of binder extracted from reclaimedasphalt such as RAP, or RAS or a combination of RAP and RAS. The steroladditive has been shown in to improve high and low temperatureproperties and PG grading for both low and high temperature ends of RAP-or RAS-containing asphalt binder blends.

The asphalt pavement material can be applied as the topmost layer of aroad pavement, with the topmost layer having an average thickness of forexample up to about 38 mm or up to about 65 mm. In some embodiments, theasphalt pavement material is applied as the topmost layer of the roadpavement, with the topmost layer having an average thickness of forexample up to about 12 mm or up to about 38 mm.

A measure of how effectively different binders respond to aging or howeffectively different additives impact the response of binders to agingis the parameter Delta Tc (ΔTc). ΔTc is calculated by subtracting them-critical temperature from the S-critical temperature. Anderson et al.in their 2011 paper showed that larger values of ΔTc were wellcorrelated to fatigue cracking of asphalt pavements. Specifically, thatresearch showed that when ΔTc was 5° C. or greater cracking was verylikely. Anderson, et al. used the procedure of subtracting theS-critical temperature from the m-critical temperature and thus the morepositive the value of ΔTc the greater the chance of fatigue cracking.Since 2011 the asphalt research community has reversed the calculationas stated above and now the more negative values of ΔTc indicatedecreasing binder performance. More recently Reinke, et al. presentedresearch at the 2016 EE Congress in Prague, Czech Republic showing thatthe more negative values of ΔTc strongly correlated to fatigue crackingon two research projects in Minnesota, USA. (Reinke, Hanz, Anderson,Impact of re-refined engine oil bottoms on binder properties and mixperformance on two pavements in Minnesota, 6th Eurasphalt and EurobitumeCongress, Prague, Jun. 1-3, 2016, DOI: dx.doi.org/10.14211/EE.2016.284).Therefore, in the industry and as used in the application, a ΔTc warninglimit value is −3° C. and a potential failure value is −5° C. In otherwords, −5° C. is more negative than −3° C. and therefore a ΔTc value of−5° C. is worse than a ΔTc value of −3° C.

To determine the ΔTc parameter, a 4 mm DSR test procedure and dataanalysis methodology from the Western Research Institute was employed asnoted above. The DSR test procedure and methodology are also disclosedin International Application No. PCT/US16/37077 filed Jun. 10, 2016, inPCT/US2016/064950 filed Dec. 5, 2016 and PCT/US2016/064961 filed Dec. 5,2016, each of which is incorporated herein by reference in its entirety.

The ΔTc parameter can also be determined using a Bending Beam Rheometer(BBR) test procedure based on AASHTO T313 or ASTM D6648. It is importantthat when the BBR test procedure is used that the test is conducted at asufficient number of temperatures such that results for the Stiffnessfailure criteria of 300 MPa and Creep or m-value failure criteria of0.300 are obtained with one result being below the failure criteria andone result being above the failure criteria. In some instances forbinders with ΔTc values less than −5° C. this can require performing theBBR test at three or more test temperatures. ΔTc values calculated fromdata when the BBR criteria requirements referred to above are not metmay not be accurate.

In embodiments, the sterol-containing asphalt binder can provide anasphalt binder composition with a ΔTc of greater than or equal to −5.0°C. In some embodiments, the sterol-containing asphalt binder can providean asphalt binder with a ΔTc of greater than or equal to −5.0° C. after27, 60, 90 and 152 hours of aging at 75° C. In still other embodiments,the sterol-containing asphalt binder can provide an asphalt binder witha less negative ΔTc value and a decreased R-Value following aging, whencompared to a similarly-aged asphalt binder without the sterol. Inembodiments, the sterol-containing asphalt binder can provide an asphaltbinder composition, a pavement, or surface treatment it is added on aΔTc of −5.0° C. to +5° C., from −4° C. to +4° C. or from −3° C. to +5°C.

Emulsions

While pavement construction can use asphalt in emulsions, emulsions aretypically used to apply asphalt surface treatments. Typical emulsionsinclude aqueous emulsions with the asphalt binder particles dispersed inwater containing one or more emulsifying agents.

The emulsifying agents used in the emulsion can include any knowncationic, anionic, nonionic, or amphoteric surfactants. In pavingapplications, asphalt emulsions are classified in ASTM D977 and D2397 bythe time it takes for “set” or “cure”: rapid setting (RS), mediumsetting (MS) or slow setting (SS). Emulsions cure through evaporation ofthe water. Some emulsions (e.g., cationic emulsions) also cure throughelectrochemical deposition of the dispersed asphalt particles on thesurface of the aggregate. This is a process of coalescence as theasphalt particles migrate to the aggregate surface and then the asphaltparticles join together or coalesce to form a uniform asphalt layer.This can be considered a chemical “break”. In any event, before anemulsion can cure or set, the emulsion typically breaks via separationof water from the asphalt particles. The breaking time is determined bythe emulsion stability, and the more stable the emulsion, the longer thebreaking time. Emulsifying agents can also be classified based on theirsurface charge (or lack thereof) as cationic, anionic, nonionic, oramphoteric. By combining the surface charge characteristic with thesetting time, emulsifiers used for paving applications can be classifiedas, for example, cationic rapid setting (CRS), cationic medium setting(CMS), and cationic slow setting (CSS). These classifications are knownin the art and can be readily measured as set forth in ASTM D977 andD2397.

The asphalt emulsions can contain other agents such as polymers,solvents and other additives as described herein.

The disclosed surface treatments are aqueous emulsions that includesterol-containing asphalt binder. The binder may be formed by mixing asterol into an asphalt binder (e.g. virgin binder). The bindercontaining sterol is then dispersed in a continuous water phase with thehelp of an emulsifying agent. The emulsifying agent and preheatedasphalt are typically pumped into a colloid mill where high shear mixingproduces an asphalt emulsion having asphalt droplets dispersed in thewater.

In micro-surfacing formulations and optionally for slurry sealoperations, the asphalt emulsions are polymer modified, e.g., toincrease the strength and durability of the resulting asphalt-based,cold paving formulations and to decrease the curing times of theseformulations.

Suitable polymer lattices for microsurfacing surface layer formulationsinclude cationic SBR (styrene-butadiene rubber) lattices, natural rubberlattices, and polychloroprene lattices (e.g., NEOPRENE™ latticesavailable from Denka Performance Elastomer LLC). SBS(poly(styrene-butadiene-styrene)) block copolymers and copolymers suchas ethylene, ethylene vinyl acetate (EVA), glycidyl methacrylateterpolymers or ethylene, n-butyl acrylate (nBA), glycidyl methacrylateterpolymers can also be used but typically must be added slowly toheated asphalt (e.g. 160-170° C.), and then subjected to high shearmixing to disperse the polymer in the asphalt prior to forming theasphalt emulsion. Commercial terpolymers that may be used includeELVALOY™ available from E. I. DuPont de Nemours.

The sterol-containing emulsion preferably includes between about 0.1 wt% and about 10 wt surfactants, 55 wt % to 95 wt % of a sterol-containingasphalt binder with water making up the total. Prior to application ofthe emulsion, the surface to be treated is usually cleaned to removeexcess surface dirt, weeds, and contaminants by, for example, brushingthe surface, blasting the surface with compressed air, or washing thesurface.

The emulsion can be applied using any suitable method for applying aliquid to a porous surface, such as brushing, wiping and drawing, orspraying. Spraying is a preferred emulsion application method because athin emulsion layer can be applied in a short time period. The emulsionis preferably applied at a temperature between 10 (15° F.) to 93° C.(200° F.) or between 15° C. (60° F.) and 87° C. (190° F.). The emulsiondesirably has a viscosity at the application temperature that allows itto be sprayed upon the surface and preferably has a viscosity of from 1to 5 centipoise.

Cold-in Place Recycling

The disclosed sterol-containing asphalt binder can also be used in anycold-in-place recycling (CIR) process known in the art. CIR involves theremoval, reprocessing and relaying of part of an existing asphaltsurface without the use of heat. CIR processes can be economical becausethey reduce costs from, for example, reusing existing material,minimizing use of new materials, decreasing material transportation andhauling demands and not heating the material. CIR can include theremoval of the top inches of an existing asphalt pavement. CIR can beused, among other things, to create a new pavement layer using the oldpavement, remove cracks, ruts and potholes and rehabilitate a pavementsurface. In some embodiments, the top 1 inch or more to the top 6 inchesor less can be removed. Removal for CIR is generally performed bymilling or grinding. Milling desirably is performed using a millingmachine or using machines referred as reclaimers.

CIR as the name implies is performed on the grade in a continuousprocess. The removed material is generally passed through a crusherwhich is component part of the CIR paving train prior to being mixedwith emulsion or foamed asphalt. The removed material can then becrushed and/or graded to produce a desired gradation. A desiredgradation can specify a maximum particle size only. One example of agradation is the removed material is less than 1¼ inch nominal size.Another example is the removed material is less than 1 inch in nominalsize. Virgin aggregate can be added to the removed material.

The material can then be mixed with an asphalt emulsion having asterol-containing asphalt binder, lime, Portland cement or fly ash. Themixing can be performed by any machine known in the art including, butnot limited to, a milling machine or a pug mill. The material can thenbe returned to the milled surface and graded. Examples of machines thatcan be used for these steps are asphalt pavers and motor graders.

Cut Backs

In some embodiments, sterol-containing asphalt binder is diluted or“cut” with solvents as part of a complex composition or network, whichmay further include functional additives such as polymers andsurfactants as well as inert additives such as filler clays andcellulose fibers. These additives are included in cutback formulationsto provide compositions with specific functional properties such asviscosity, elasticity adhesion and cure rate.

Cutbacks are used because their viscosity is lower than that of neatasphalt and can thus be used in low temperature applications. After acutback is applied, the solvent evaporates at different rates dependingon the volatility of the solvent used to produce the cutback. As thesolvent evaporates the viscosity of the remaining asphalt binderincreases resulting in an increasingly stable mixture with aggregate. Acutback asphalt is said to “cure” as the petroleum solvent evaporatesaway.

Exemplary cutback solvents include petroleum solvents, Light Cycle Oil(LCO) and #2 Diesel Fuel. naphtha, #1 oil, or #2 oil, to name a few.

The types of cutback asphalts are defined by American Society of Testingand Materials (ASTM) specifications as follows:

SC=Slow cure type (Road Oils): ASTM D-2026-72

MC=Medium cure type: ASTM D-2027-76

RC=Rapid cure type: ASTM D-2028-76

The cutback may for example contain from 50 to 96 wt % asphalt binder,70 to 90 wt % asphalt binder, or 75 to 85% asphalt binder, with theremainder being cutback solvent. In addition, the cutback asphalt maycontain conventional amounts of antistrip or other additives.

Interlayers

The disclosed sterol-containing asphalt binder can also be used aninterlayer. FIG. 1C illustrates interlayers as layers that maybe placedbetween an old asphalt pavement and a newly applied asphalt layer.Interlayers are typically an asphalt mix with a high binder amount.

In one exemplary embodiment, an interlayer mix contains 6% to 12%polymer modified binder and 88% to 94% crushed aggregate. The binder isproduced by modifying a blend of virgin binder and 0.5% to 15% sterolwith an elastomer. Examples of materials requirements can be found atthe Iowa DOT specification SS-15006, “Supplemental Specifications forHot Mix Asphalt Interlayer.” In some embodiments, the asphalt binder(polymer modified or not) contains the disclosed sterol.

EXAMPLES

The following study showed that the presence of sterol in a base asphaltbinder used to produce an emulsion retards the aging of the binder inthe top ½ inch of mix in compacted specimens relative to the untreatedand only compacted specimens.

Specimens of bituminous mixtures used were Wisconsin specification 3million Equivalent Single Axel Load (ESAL) mixture containing ReclaimedAsphalt Pavement (RAP) yielding a 0.2 binder replacement ratio using(4.5% by weight) virgin PG 58S-28 asphalt binder for a total bindercontent of 5.6%. These bituminous mixtures were compacted to a targetair voids level of 6% to 8% using two gyratory compactors referenced bythe prefix T and P. The gyratory compactors referenced T weremanufactured by Troxler Electronic Laboratories, Inc. of ResearchTriangle Park, N.C. The gyratory compactors referenced P weremanufactured by Pine Instrument Company of Grove City, Pa.

All specimens were compacted to a height of 95 mm and a diameter of 150mm. All specimens were inserted into sleeves of approximately 97 mm inheight cut from 6 inch internal diameter sewer pipe with a nominal ⅛inch wall thickness. The tops and bottoms of the specimens remainedexposed. The compacted specimens were separated into three groups, eachgroup having 20 specimens (10 T and 10 P). Group I of twenty specimensreceived no treatment and was oven aged or naturally aged. Group II oftwenty specimens was treated with the equivalent of 0.2 gallons/yd² of acationic quick set (CQS) emulsion produced from a PG 64S-22 base binder.Group III of twenty specimens was treated with the equivalent of 0.2gallons/yd² of a cationic quick set (CQS) emulsion produced from a PG64S-22 to which 5% phytosterol had been added prior to emulsification.The percent residue of the CQS emulsion was in each case between 65% and66%. A foam brush was used to apply the emulsion by weight to the topsof the gyratory specimens that had been inserted into the sewer pipe.The tops of the gyratory specimens were the tops of the compactedspecimens as removed from the gyratory molds. The air voids of allspecimens were determined using AASHTO T-166 and recorded for the uniquealpha numerical identifier assigned to each specimen. The outside of thesewer pipe containing each specimen was labeled as “untreated”, “CQS”,or “CQS+sterol” as well as being labeled with a T or P followed by theunique numerical identifier assigned to that particular specimen.

The three groups of twenty specimens per group were further separatedinto three groups of ten specimens. Each sub group of ten specimenscontained 10 untreated specimens, 10 CQS treated specimens and 10CQS+sterol treated specimens and each group of 10 specimens containedfive T and five P specimens. One subgroup of thirty specimens was placedin a forced draft oven held at 75° C. for aging and the other subgroupof thirty specimens was placed out in the open to be aged naturally. Theoven conditioned samples were removed from the oven after 27, 60, 90,and 152 days of conditioning at 75° C.

Accelerating aging by oven conditioning the samples stimulates as muchas possible the real world conditions of pavements. In the real worldconditions, temperature of a pavement layer decreases with increasingdepth from the surface. By encasing the test samples in PVC sleeves,this would prevent oxygen from moving through the sidewalls of thesamples and thereby stimulate a real world condition for pavements.

Tables 1 through 5 summarize the data obtained by testing binder samplesrecovered from top ½ inch layer of the compacted mixture specimens forthe untreated, CQS emulsion, and CQS emulsion produced from asphaltcontaining 5% of plant sterols.

Table 1 is the base or control data for all the treatments. Table 1 datawas recovered from a compacted mix specimen, which received no treatmentand had not been aged.

TABLE 1 Properties of Recovered Binder with no Treatment and no AgingProperties Of Recovered Binder From Sample With No Aging PG PG S- m-Grade Grade critical critical Sample @ 1.0 kPa, @ 2.2 kPa, Temp, Temp,ΔTc, R- ID Description ° C. ° C. ° C. ° C. ° C. Value Control control,Top 87.1 80.5 −29.74 −28.62 −1.13 2.621 0.5″, T-30, P-15, Rec AC, 4 mm,HR3-4 no aging

The data in Tables 2 through 5 summarize the recovered binder data after27, 60, 90, and 152 days of aging at 75° C. in a forced draft oven. Boththe PG Grade at 1.0 kPa and 2.2 kPa provide an indication of therelative change in binder stiffness. The higher the temperature at whichthe binder achieves a stiffness of 1.0 kPa or 2.2 kPa the more aged thatbinder has become. The low temperature Stiffness Critical temperature(S-critical) and the relaxation critical temperature (m-critical) trackthe change in the low temperature grade of the recovered binder. Thesevalues were determined using a 4 mm dynamic shear rheometer testfollowing the procedure of Sui, et al. referenced in this application.The parameter labeled ΔTc is determined by subtracting the m-criticalvalue from the S-critical value. The more negative the ΔTc resultbecomes the more susceptible to fatigue cracking the mixture containingthat binder becomes. Values of ΔTc less than −5° C. for a binder areindicative of mixture susceptible to fatigue cracking. The R-valueparameter is an indication of the ability of a binder to relax stress.Binders with higher R-values have more trouble relaxing stress andconsequently are more prone to cracking.

TABLE 2 Properties of Recovered Binder from the top ½ inch of thecompacted specimens for all Treatments after 27 Days of Aging at 75° C.Properties Of Recovered Binder After 27 Days Mix Aging @ 75° C. S- m- PGGrade PG Grade critical critical Sample @ 1.0 kPa, @ 2.2 kPa, Temp,Temp, ΔTc, R- ID Description ° C. ° C. ° C. ° C. ° C. Value 1 Untreated,27 days at 89.8 83.8 −28.32 −25.05 −3.27 2.802 75°, T-1, P-33, Top 0.5″,Rec AC, 4 mm, HR3-4-2 2 CQS−No Sterol, 27 85.9 79.7 −29.03 −27.39 −1.642.532 days at 75°, T-5, P-3, Top 0.5″, Rec AC, 4 mm, HR3-4 3 CQS+Sterol,27 days 84.3 77.9 −28.77 −28.24 −0.53 2.283 at 75°, T-7, P-19, Top 0.5″,Rec AC, DSR, HR3-3

TABLE 3 Properties of Recovered Binder from the top ½ inch of thecompacted specimens for all Treatments after 60 Days of Aging at 75° C.Properties Of Recovered Binder After 60 Days Mix Aging @ 75° C. S- m- PGGrade PG Grade critical critical sample @ 1.0 kPa, @ 2.2 kPa, Temp,Temp, ΔTc, R- ID Description ° C. ° C. ° C. ° C. ° C. Value 4 Untreated,60 days@ 92.8 86.4 −25.65 −19.96 −5.69 3.098 75° C., T-11, P-29, Top0.5″, 4 mm, HR3-2 5 CQS−No Sterol 60 93.1 87.0 −26.80 −20.35 −6.46 3.008days@ 75° C., T-13, P- 11, Top 0.5″, 4 mm, HR3-3 (1) 6 CQS+Sterol, 6091.0 84.8 −26.96 −23.42 −3.54 2.720 days@ 75° C., T-19, P- 20, Top 0.5″,4 mm, HR3-3 (1)

TABLE 4 Properties of Recovered Binder from the top ½ inch of thecompacted specimens for all Treatments after 90 Days of Aging at 75° C.Properties Of Recovered Binder After 90 Days Mix Aging @ 75° C. m- PGGrade PG Grade S-critical critical sample @ 1.0 kPa, @ 2.2 kPa, Temp,Temp, ΔTc, R- ID Description ° C. ° C. ° C. ° C. ° C. Value 7 Untreated90 Days 101.6 95.2 −24.99 −17.09 −7.89 3.304 @75° C., T15&P7, Top 0.5″,4 mm, HR3-2 T- avg 8 CQS− No Sterol, 90 97.9 91.4 −25.06 −18.38 −6.673.125 days @ 75° C., T-8, P- 16, Top 0.5″, Rec AC, 4 mm, HR3-1 T-avg 9CQS+ sterol, 90 days 98.1 91.2 −23.96 −19.07 −4.89 2.939 @ 75° C., T-21,P-25, Top 0.5″, Rec AC, 4 mm, HR3-1 T-avg

TABLE 5 Properties of Recovered Binder from the top 1/2 inch of thecompacted specimens for all Treatments after 152 Days of Aging at 75° C.Properties Of Recovered Binder After 152 Days Mix Aging @ 75° C. S- m-PG Grade PG Grade critical critical Sample @ 1.0 kPa, @ 2.2 kPa, Temp,Temp, ΔTc, R- ID Description ° C. ° C. ° C. ° C. ° C. Value 10 Untreated152 Days 118.8 111.8 −20.57 −5.66 −14.91 3.943 @75° C., T24&P10, Top0.5″, 4 mm, HR3-2 T-avg 11 CQS− No Sterol, 152 111.4 104.5 −21.92 −10.09−11.83 3.658 days @ 75° C., T-23, P-18, Top 0.5″, Rec AC, 4 mm, HR3-2 T-avg 12 CQS+ sterol, 152 108.6 101.9 −21.95 −12.81 −9.14 3.299 days @ 75°C., T-28, P-27, Top 0.5″, Rec AC, 4 mm, HR3-1 T- avg

The data summarized in these tables show that the binders recovered fromthe specimens treated with the CQS emulsion produced from the basebinder with 5% sterol have the lowest values of m-critical temperatures,the least negative values of ΔTc and lowest R-values compared to theother two treatments. At every aging step the sterol containingtreatment retarded the impact of aging resulting from conditioningtemperature and oxidative hardening.

FIGS. 2 to 6 show the data from Tables 1 through 5 plotted for easierinterpretation. For aged asphalt binders the low temperature m-criticalvalue (FIG. 2 ) is the low temperature PG grade of the binder. Them-critical temperature is obtained from the slope measured at 60 secondsof the relaxation modulus master curve. The m-critical slope value canbe obtained from the Bending Beam Rheometer or test (ASTM D6648) or fromthe 4 mm DSR test as shown by the research of Sui and Farrar at WesternResearch Institute. The more readily a binder can relax stresses thelower will be binder failing temperature. The sterol addition showedimproving the ability of the binder to relax stresses at low andintermediate temperatures.

FIG. 3 is a plot of the low temperature S-critical or Stiffness Criticalvalue at the different aging times. FIG. 3 shows that there is minorvariation in the S-critical values between treatments at any given agingtime. It is also worth emphasizing that although the S-criticaltemperatures are colder than the m-critical temperatures the PG binderspecifications for the low temperature failing grade of the binder isbased on the warmer of these two low temperature values. Therefore, ifan additive can slow down the rate at which the m-critical valuedegrades then the binder will have better low temperature performance.

FIG. 4 is a plot of the ΔTc value at the different aging times. FIG. 4shows that initially (at 27 days) the addition of both the CQS andCQS+sterol emulsions to the mix specimens improved the ΔTc values forthose two treatments relative to the original ΔTc at zero time. Therecovered binder for the untreated samples shows that ΔTc decreased bymore than 2° C., whereas ΔTc for the plain CQS treated samples decreasedonly about 0.5° C. The ΔTc value for the CQS+sterol treated samplesincreased by 0.6° C. The additional asphalt binder added to the originalspecimens accounted for a reduced rate of aging for the CQS treatedspecimens and the additional asphalt binder plus the impact of thesterol accounted for the improvement of the recovered binder after 27days of aging relative to the ΔTc of zero-day aged mix. After both 60and 90 days of aging the ΔTc values of binder recovered from theCQS+sterol treated specimens were still greater than −5° compared to ΔTcfor the untreated and CQS treated specimens. Even after 152 days ofaging the CQS+sterol treated specimens have a better ΔTc value comparedto the other treatments.

FIG. 5 is a plot of the binder Rheological index or R-Value for thedifferent treatments. The R-value is another indicator of the ability ofa binder to relax stress. Binders with increasing R-Values havedecreased ability to relax stress. It is desirable to keep R-Value under3 and as FIG. 5 shows the initial application of the emulsion treatmentsreduced the R-values for those two treatments, but by 60 hours of agingthe untreated and CQS treated specimens had values greater than 3.Through the entire aging sequence, the CQS+sterol treated specimens hadconsistently better R-values than the other treatments.

FIG. 6 is a plot of the high temperature PG grade of binders recoveredfrom the various treatments with aging time. The data shows relativelyminor variation in high temperature grade with aging; however, theCQS+sterol treatment does consistently have the lowest high temperaturevalue. The high temperature property of the binder is not highlysignificant as long as the binder is stiff enough to resist rutting andfor a typical upper Midwestern US climate, all of these binders possesssufficient stiffness.

Tables 6 and 7 show the properties of binders recovered from the 2nd ½inch of the compacted specimens after 60 and 152 days of aging. Thepurpose of obtaining this data at these intervals was to show the agingof the binder in these layers compared to aging of the binder in the top½ inch mixture layers. With the exception of the ΔTc value for the 2nd ½inch binder from the untreated specimen the properties of theserecovered binders at 60 days and at 152 days are similar. The 60 dayuntreated sample with a ΔTc of −3.80° C. may be due to the warmerS-critical value for the untreated sample compared to the CQS andCQS+sterol treatments. A warmer S-critical value indicates a greateraging of the stiffness failure temperature compared to the treatedsamples and could be due to more oxygen migration into the 2nd ½ inch ofthe mix. Because the untreated samples did not have any emulsiontreatment, the surface half inch of those untreated specimens would havea greater opportunity for oxygen to permeate the mix. The R-value forthe untreated 60 day recovered binder is similar to the other twotreatments which is consistent with similar properties of relaxation andalso consistent with the similarities of the m-critical properties ofall three treatments for the 2nd ½ inch recovered binders.

FIG. 7 shows bar chart comparisons of the S-critical and m-critical databetween the top ½ inch and second ½ inch recovered binder at 60 days ofaging. FIG. 8 shows comparison between the ΔTc and R-Value propertiesfor the same binders at 60 days of aging. FIGS. 9 and 10 show similarrespective plots for the binders recovered from the top and second ½inch of binders recovered after 152 days of aging.

The S-critical values show hardly any variation with respect to depthfor any treatment and the m-critical value for the top ½ inch of theCQS+sterol treatment exhibits a 2.4° C. better low temperaturem-critical value than the binder from the 2nd half inch. The fact thatthe CQS treated specimens exhibited an m-critical value 0.6° C. betterthan the second half inch recovered binder shows that the additionalbinder added to the mix was not the source of the more greatly improvedm-critical value in the CQS+sterol specimens and shows that the fog sealapplication of the emulsion containing the sterol resides in the tophalf inch layer.

The data plotted in FIG. 8 shows ΔTc values for the top half inch andsecond half inch binders after 60 days. The R-value for the top halfinch of the sterol treated mix was also lower than the second half inch.

FIG. 9 shows S-critical and m-critical comparisons after 152 days ofaging. The S-critical data is very similar for all treatments for bothlayers. The m-critical values show definite differences. The second halfinch layers were very similar with the untreated specimens having aslightly warmer m-critical temperature. The CQS treated specimens had am-critical value 2.67° C. cooler (i.e. better) for the top half inchcompared to the second half inch (−10.09° C. vs. −7.42° C.). This isattributable to the extra asphalt added in the fog seal. The top halfinch of the CQS+sterol however had an m-critical value that was 2.7° C.cooler (i.e. better) than the CQS only treatment and 5.7° C. cooler(i.e. better) than the second layer of the CQS+sterol treatmentspecimens. This shows that sterol treated specimens resides in the tophalf inch. The CQS treated results also show that the fog seal treatmentin general resides in the top half inch while at the same timeemphasizing that just applying the asphalt emulsion does not provide thesame age retarding benefits as having the sterol additive present in thetreatment.

FIG. 10 compares the ΔTc and R-values for the three treatments after 152days of conditioning. The ΔTc values for both layers of the untreatedspecimens and the second half-inch of the CQS and CQS+sterol treatmentsare all similar with the emulsion treated specimens being slightlybetter, most likely due to the asphalt added to the surface of thosespecimens. The CQS treated specimens had a top half-inch layer ΔTc 2.2°C. better than the second half-inch binder, but the CQS+sterol top halfinch layer ΔTc was 5° C. better than the second half inch layer. TheR-value data also shows similar relative performance. The untreatedspecimens have nearly identical R-values, the CQS treated specimens showthat the top half inch binder has a 0.25 R-value improvement over thesecond half inch binder and the CQS+sterol treated specimens have a tophalf inch binder has a 0.74 R-value improvement over the binder in thesecond half inch.

What is claimed is:
 1. A method for slowing the aging rate of anexisting asphalt-containing pavement comprising: applying asterol-containing asphalt binder emulsion to the surface of the existingasphalt-containing pavement; wherein the asphalt binder emulsioncomprises asphalt binder and 0.5 to 15 wt. % of a sterol additive basedon the asphalt binder weight; and curing the applied sterol-containingasphalt binder emulsion to form a surface treatment on the existingasphalt-containing pavement, said surface treatment comprising thesterol additive, wherein the sterol additive in the surface treatmentretards or slows the aging rate of the underlying existingasphalt-containing pavement, and wherein the sterol additive comprises asterol blend of 10:90 ratio by weight to 90:10 ratio by weight of puresterol:crude sterol.
 2. The method of claim 1, wherein the steroladditive is 1 to 10 wt. % of the asphalt binder weight.
 3. The method ofclaim 1, wherein the sterol additive comprises cholesterol.
 4. Themethod of claim 3, wherein the pure sterol comprises a blend of plantsterol and cholesterol.
 5. The method of claim 1, wherein the crudesterol additive comprises a plant sterol source.
 6. The method of claim5, wherein the crude sterol source comprises a tall oil pitch.
 7. Themethod of claim 1, wherein the existing pavement comprises reclaimedasphalt binder from recycled asphalt pavement (RAP), recycled asphaltshingles (RAS), a softening agent, or combinations thereof.
 8. Themethod of claim 1, wherein the sterol-containing asphalt binder providesa ΔTc of greater than or equal to −5.0° C.
 9. A road surface made fromthe method of claim
 1. 10. The method of claim 1, wherein the surfacetreatment is applied as the asphalt binder component of a chip seallayer.
 11. The method of claim 1, wherein the surface treatment isapplied as a fog seal.
 12. The method of claim 1, wherein the surfacetreatment is applied as a tack coat.
 13. The method of claim 1, whereinthe surface treatment reduces surface cracking of the existing asphaltpavement or reduces moisture uptake of the existing asphalt pavement.14. The method of claim 1, wherein the sterol-containing asphalt binderemulsion is applied to the surface of the existing pavement as anasphalt binder component of a thinlay having a thickness of about 12 mm(0.5 inches) to about 38 mm (1.5 inches).
 15. The method of claim 1,wherein the surface treatment is applied to the surface of the existingpavement as an asphalt binder component of a thinlay having a thicknessof 12 mm (0.5 inches) to about 19 (0.75 inches) mm.
 16. The method ofclaim 1, wherein the sterol additive comprises campesterol, stigasterol,stigmasterol, β-sitosterol, Δ5-avenosterol, Δ7-stigasterol,Δ7-avenosterol, brassicasterol or mixtures thereof.